Send to

Choose Destination
See comment in PubMed Commons below
Protein Sci. 2003 Jun;12(6):1145-57.

The role of alpha-, 3(10)-, and pi-helix in helix-->coil transitions.

Author information

Department of Medicinal Chemistry, University of Washington, Seattle, Washington 98195, USA.


The conformational equilibrium between 3(10)- and alpha-helical structure has been studied via high-resolution NMR spectroscopy by Millhauser and coworkers using the MW peptide Ac-AMAAKAWAAKA AAARA-NH2. Their 750-MHz nuclear Overhauser effect spectroscopy (NOESY) spectra were interpreted to reflect appreciable populations of 3(10)-helix throughout the peptide, with the greatest contribution at the N and C termini. The presence of simultaneous alphaN(i,i + 2) and alphaN(i,i + 4) NOE cross-peaks was proposed to represent conformational averaging between 3(10)- and alpha-helical structures. In this study, we describe 25-nsec molecular dynamics simulations of the MW peptide at 298 K, using both an 8 A and a 10 A force-shifted nonbonded cutoff. The ensemble averages of both simulations are in reasonable agreement with the experimental helical content from circular dichroism (CD), the (3)J(HNalpha) coupling constants, and the 57 observed NOEs. Analysis of the structures from both simulations revealed very little formation of contiguous i --> i + 3 hydrogen bonds (3(10)-helix); however, there was a large population of bifurcated i --> i + 3 and i --> i + 4 alpha-helical hydrogen bonds. In addition, both simulations contained considerable populations of pi-helix (i --> i + 5 hydrogen bonds). Individual turns formed over residues 1-9, which we predict contribute to the intensities of the experimentally observed alphaN(i,i + 2) NOEs. Here we show how sampling of both folded and unfolded structures can provide a structural framework for deconvolution of the conformational contributions to experimental ensemble averages.

[Indexed for MEDLINE]
Free PMC Article
PubMed Commons home

PubMed Commons

How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for Wiley Icon for PubMed Central
    Loading ...
    Support Center